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Characterization of Apricot pseudo-chlorotic leaf spot virus, A Novel Trichovirus Isolated from Stone Fruit Trees

First, fifth, and sixth authors: Dipartimento di Arboricoltura, Botanica e Patologia Vegetale, Università degli Studi di Napoli Federico II, 80055 Portici, Napoli, Italy; second, third, fourth, and eighth authors: Equipe de Virologie, UMR GD2P, INRA et Université Bordeaux 2, IBVM, Campus INRA, BP81, 33883 Villenave d'Ornon Cedex, France; and seventh author: Department of Primary Industries, 621 Burwood Highway, Knoxfield, Victoria, 3156 Australia

A trichovirus closely related to Apple chlorotic leaf spot virus (ACLSV) was detected in symptomatic apricot and Japanese plum from Italy. The Sus2 isolate of this agent cross-reacted with anti-ACLSV polyclonal reagents but was not detected by broad-specificity anti- ACLSV monoclonal antibodies. It had particles with typical trichovirus morphology but, contrary to ACLSV, was unable to infect Chenopodium quinoa and C. amaranticolor. The sequence of its genome (7,494 nucleotides [nt], missing only ≈30 to 40 nt of the 5′ terminal sequence) and the partial sequence of another isolate were determined. The new virus has a genomic organization similar to that of ACLSV, with three open reading frames coding for a replication-associated protein (RNA-dependent RNA polymerase), a movement protein, and a capsid protein, respectively. However, it had only ≈65 to 67% nucleotide identity with sequenced isolates of ACLSV. The differences in serology, host range, genome sequence, and phylogenetic reconstructions for all viral proteins support the idea that this agent should be considered a new virus, for which the name Apricot pseudo-chlorotic leaf spot virus (APCLSV) is proposed. APCLSV shows substantial sequence variability and has been recovered from various Prunus sources coming from seven countries, an indication that it is likely to have a wide geographical distribution.